title: Constitutive Mad1 targeting to kinetochores uncouples checkpoint signalling from chromosome biorientation.
abstract: Accurate chromosome segregation depends on biorientation, whereby sister chromatids attach to microtubules from opposite spindle poles. The spindle-assembly checkpoint is a surveillance mechanism in eukaryotes that inhibits anaphase until all chromosomes have bioriented. In present models, the recruitment of the spindle-assembly checkpoint protein Mad2, through Mad1, to non-bioriented kinetochores is needed to stop cell-cycle progression. However, it is unknown whether Mad1-Mad2 targeting to kinetochores is sufficient to block anaphase. Furthermore, it is unclear whether regulators of biorientation (for example, Aurora kinases) have checkpoint functions downstream of Mad1-Mad2 recruitment or whether they act upstream to quench the primary error signal. Here, we engineered a Mad1 construct that localizes to bioriented kinetochores. We show that the kinetochore localization of Mad1 is sufficient for a metaphase arrest that depends on Mad1-Mad2 binding. By uncoupling the checkpoint from its primary error signal, we show that Aurora, Mps1 and BubR1 kinases, but not Polo-like kinase, are needed to maintain checkpoint arrest when Mad1 is present on kinetochores. Together, our data suggest a model in which the biorientation errors, which recruit Mad1-Mad2 to kinetochores, may be signalled not only through Mad2 template dynamics, but also through the activity of widely conserved kinases, to ensure the fidelity of cell division.
authors.affiliation: Laboratory of Chemistry and Cell Biology, The Rockefeller University, New York, New York 10065, USA.
authors.forename: Maria
authors.initials: M
authors.lastname: Maldonado
authors.forename: Tarun M
authors.initials: TM
authors.lastname: Kapoor
mesh_terms: D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D020090:Chromosome Segregation; D006367:HeLa Cells; D006801:Humans; D018386:Kinetochores / Q000378:metabolism*; D064246:Mad2 Proteins; D008870:Microtubules / Q000378:metabolism; D008938:Mitosis / Q000502:physiology*; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D008941:Spindle Apparatus / Q000378:metabolism*
chemical_list: D002135:Calcium-Binding Proteins; D018797:Cell Cycle Proteins; C501384:MAD1L1 protein, human; C577697:MAD2L1 protein, human; D064246:Mad2 Proteins; D009687:Nuclear Proteins; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins